Ziegler-Natta (ZN) type polyolefin catalysts are well known in the field of polymers, generally, they comprise (a) at least a catalyst component formed from a transition metal compound of Group 4 to 6 of the Periodic Table (IUPAC, Nomenclature of Inorganic Chemistry, 1989), a metal compound of Group 1 to 3 of the Periodic Table (IUPAC), and, optionally, a compound of group 13 of the Periodic Table (IUPAC) and/or an internal donor compound. ZN catalyst may also comprise (b) further catalyst component(s), such as a cocatalyst and/or an external donor.
Various methods for preparing ZN catalysts are known in the state of art. In one known method, a supported ZN catalyst system is prepared by impregnating the catalyst components on a particulate support material. In WO-A-01 55 230, the catalyst component(s) are supported on a porous, inorganic or organic particulate carrier material, such as silica.
In a further well known method the carrier material is based on one of the catalyst components, e.g. on a magnesium compound, such as MgCl2. This type of carrier material can also be formed in various ways. EP-A-713 886 of Japan Olefins describes the formation of MgCl2 adduct with an alcohol which is then emulsified and finally the resultant mixture is quenched to cause the solidification of the droplets.
Alternatively, EP-A-856 013 of BP discloses the formation of a solid Mg-based carrier, wherein the Mg-component containing phase is dispersed to a continuous phase and the dispersed Mg-phase is solidified by adding the two-phase mixture to a liquid hydrocarbon.
The formed solid carrier particles are normally treated with a transition metal compound and optionally with other compounds for forming the active catalyst.
Accordingly, in case of external carriers, some examples of which are disclosed above, the morphology of the carrier is one of the defining factors for the morphology of the final catalyst.
One disadvantage encountered with the supported catalyst systems is that distribution of the catalytically active compounds on the support material is dependent on the surface chemistry and the surface structure of the support material. As a result this may often lead to non-uniform distribution of the active component(s) within the catalyst particle. As a consequence of the uneven distribution of the active sites in catalyst particles catalysts with intra-particle in-homogeneities, as well inter-particle in-homogeneities between separate particles are obtained, which leads finally to in-homogeneous polymer material.
Further, support material will remain in the final polymer as a residue, which might be harmful in some polymer applications.
WO-A-00 08073 and WO-A-00 08074 describe further methods for producing a solid ZN-catalyst, wherein a solution of an Mg-based compound and one or more further catalyst compounds are formed and the reaction product thereof is precipitated out of the solution by heating the system. Furthermore, EP-A-926 165 discloses another precipitating method, wherein a mixture of MgCl2 and Mg-alkoxide is precipitated together with a Ti-compound to give a ZN catalyst.
EP-A-83 074 and EP-A-83 073 of Montedison disclose methods for producing a ZN catalyst or a precursor thereof, wherein an emulsion or dispersion of Mg and/or Ti compound is formed in an inert liquid medium or inert gas phase and said system is reacted with an Al-alkyl compound to precipitate a solid catalyst. According to examples said emulsion is then added to a larger volume of Al-compound in hexane and prepolymerised to cause the precipitation.
In general, a drawback of such precipitation methods is the difficulty to control the precipitation step and thus the morphology of the precipitating catalyst particles. Furthermore, the precipitation of the catalyst component(s) results easily in formation of broad particle size distribution of catalyst particles comprising particles from very small particles to big agglomerates, and further to the loss of the morphology of the catalyst and formation of fines. In polymerisation process this causes in turn undesired and harmful disturbances, like plugging, formation of polymer layer on the walls of the reactor and in lines and in further equipments, like extruders, as well decreased flowability of polymer powder and other polymer handling problems.
WO 03/000757 as well WO 03/000754 describe a process for the preparation of an olefin polymerisation catalyst component, enabling to prepare solid particles of a catalyst component comprising a group 2 metal together with a transition metal however without using any external carrier material or without using conventional precipitation methods, but using so called emulsification-solidification method for producing solid catalyst particles. In this process a phthalate type internal electron donor is prepared in situ during the catalyst preparation in a way and using chemicals so that a stable emulsion is formed. Droplets of the dispersed phase of the emulsion form the catalyst component, and solidifying the droplets results in solid particulate catalyst.
WO 2004/029112 discloses a further modification of the basic emulsion-solidification method as described in WO 03/000757 as well WO 03/000754, and relates thus to process for preparing an olefin polymerisation catalyst component, wherein the process is further characterized in that a specific aluminum alkyl compound is brought into contact with the catalyst component, enabling a certain degree of activity increase at higher temperatures.
U.S. Pat. No. 5,413,979 describe a further method for the preparation of a solid procatalyst composition wherein support materials are impregnated with catalyst component precursors in order to obtain a catalyst component.
U.S. Pat. No. 4,294,948 finally discloses a process for preparing an olefin polymer or copolymer, employing a solid titanium catalyst component prepared by treating pulverized catalyst precursors with organo metallic compounds of a metal of any of groups I or III of the Periodic Table, characterized in that the catalyst preparation occurs using pulverized, solid and particulate precursor materials.
EP 1403292 A1, EP 0949280 A1, U.S. Pat. Nos. 4,294,948, 5,413,979,and 5,409,875 as well as EP 1273595 A1 describe processes for the preparation of olefin polymerisation catalyst components or olefin polymerisation catalysts as well as processes for preparing olefin polymers or copolymers.
Accordingly, although much development work has been done in the field of Ziegler-Natta catalysts, there remains a need for alternative or improved methods of producing ZN catalysts with desirable properties. One particular aspect in this connection is the desire to avoid as far as possible the use of substances which are considered as potential harmful compounds regarding health as well as environmental aspects. One class of substances which have been considered as potential harmful compounds is phthalates, which have been commonly used as internal electron donors in Ziegler-Natta type catalysts. Although the amount of these phthalate compounds, used as internal donors in catalysts, in the final polymer is very small, it is still desirable to find out alternative compounds to replace phthalate compounds and still get catalysts having good activity, excellent morphology and other desired properties.
Use of non-phthalate donors is as such not new in ZN catalysts. However, such donors are used in catalysts, which are prepared by precipitation method (as in WO2009/057747 or U.S. Pat. No. 6,521,560) or supporting the catalyst components on an external carrier. Drawbacks of such catalysts are described above.
The above-outlined prior art procedures, in particular the processes for preparing olefin polymerisation catalyst components as outlined in WO 03/000757 (emulsion (liquid/liquid two-phase system)-solidification method) typically comprise bis(2-ethyl-hexyl)phthalate (often called dioctylphthalate, DOP) as internal donor. The process for preparing such catalyst components involves the preparation of the donor in situ by reacting a precursor of this internal donor, typically phthaloyldichloride (PDC), with an alcohol, typically 2-ethyl-hexanol, which has been essential in forming the stable liquid-liquid-two phase system and results in excellent morphology and desired mean particle size of the catalyst and in addition activity on a desired level.
Accordingly, it would be highly advantageous if processes for preparing olefin polymerisation catalyst components would be available which allow the formation of catalyst components via the liquid-liquid two-phase system as for example outlined in WO 03/000757, however without the need of using non-desired phthalate compounds in catalyst preparation, and still get the excellent properties obtainable by the emulsion-solidification method. Until now it has not been possible, i.e. it has not been possible to form a stable emulsion just by changing a donor or donor precursor, due to the very sensitive nature of emulsion formation in this catalyst preparation method.
It is of particular interest to obtain a catalyst in particulate form which results in good and desired polymer properties, which catalysts and further polymers are free of such undesired substances, especially phthalate compounds or their derivatives. Accordingly it is one object of the present invention to provide a method for preparing catalyst components which do not require the use of phthalates as internal electron donor and still without sacrificing the desired and advantageous properties of the known catalyst components. Further, it is an object of the invention to provide a catalyst as herein described for use in olefin polymerisation.